1. Field of the Invention
This invention pertains to the general field of video display controllers or raster scan display controllers which are used in computer systems. In particular it pertains to a logic circuit which is used to expand a monochrome image to a color image while minimizing memory storage requirements for a multicolor display.
2. Description of the Prior Art
Most presently available video display systems typically include a processor, a video controller, a display memory containing a single current screen image, other system memory, and a raster scan video display. In normal (steady-state) operation, the video controller continually reads out the contents of the display memory and transforms the information read into signals which control the raster scan beam during its active display time. The video controller also provides the horizontal and vertical retrace signals at appropriate intervals, and blanking of the raster scan beam during retrace.
The processor also has access to the display memory, so that it can change the current screen image. This access may either be "through" the video controller or "around" it. The subject invention applies to the former type of system. In either case, use of the display memory typically involves careful control of updating and display accesses to prevent image breakup while the video image is being changed.